This invention relates to the distribution of cutting teeth in boring apparatus useful, e.g., in earth or rock, and in particular in such apparatus in which the surface swept by the teeth during operation is oblique to the direction of overall advance of the apparatus, as in the generally conically shaped apparatus disclosed in my copending patent application Ser. No. 448,245, filed Mar. 5, 1974, now U.S. Pat. No. 3,897,837, the disclosure of which is hereby incorporated by reference.